You are working for Google !

All of us using  reCaptcha™ are scanning a book, one word at a time !

 

From the Google Blogoscoped blog (emphasis added) :

 

“ Technically, here’s how reCaptcha works. Captchas (short for Completely Automated Public Turing test to tell Computers and Humans Apart) are deliberately distorted to make them hard to read, so that they can’t be easily solved with existing OCR algorithms. At reCaptcha – which webmasters can easily plug-in to their existing forms and configure via e.g. a JavaScript API – you’ll always be presented with two, not just one words. The trick is that reCaptcha already knows one of the words, but wants you to help solve the other word (if enough other people solve that other word similarly, the system gains confidence that it now knows what that word reads). So you can say one word is the actual Captcha test word... while the other word deliberately spends more of your time than needed for the robot test by letting you turn books into text. It’s these extra seconds that you spend solving the secondary, unknown word that make up the CPU of that crowd computer Google now owns. “